This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. To advance the hypothesis that the structure of an individual optic nerve head (ONH) determines the level of intra ocular pressure (IOP) at which damage occurs, parallel linear finite element (FE) computations are carried out on micron-scale voxel-based 3D ONH reconstructions of the laminar connective tissue (LCT) from three normal monkey eyes. A pressure load corresponding to an IOP increase from 10 to 45 mmHg was applied directly to the anterior surface of elastically weak neural tissue encapsulating the LCT. In addition,the IOP-induced scleral canal expansion (SCE) was applied to the LC at its scleral canal wall insertion, as obtained from a macro-scale continuum FE model of the entire posterior pole of the same eye pressurized from 10 to 45 mmHg. The LCT's Young's modulus was determined by fitting its average posterior displacement to experimental data. In one of the normal eyes (with ~4 million elements): Regional mean values of LC (von Mises) stress and (maximum principal) strain were strongly correlated. Generally, IOP alone caused stress and strain to increase with depth into the LC centrally, but decrease peripherally. Generally, SCE alone induced the opposite behavior. The combined effects of IOP and SCE induced maximum stress and strain midway through the thickness of the LC in both the central and peripheral regions, and caused LC thinning by 2.8% centrally and 5.5% peripherally. The same loading methodology when applied to a contralateral pair of normal monkey eyes (with 12/13.5 million elements) showed smaller magnitudes of the strain in the superior regions of both eyes as compared to other regions. Sensitivity of these results to small changes in neural tissue modulus and the estimated deviation of the full strain from the linearized strain suggests the need to include geometric non-linearity in the model.
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